Modern mobile telecommunications standards continue to demand increasingly greater rates of data exchange (data rates). One way to achieve a high data rate in a mobile device is through the use of carrier aggregation. Carrier aggregation allows a single mobile device to aggregate bandwidth across one or more operating bands in the wireless spectrum. The increased bandwidth achieved as a result of carrier aggregation allows a mobile device to obtain higher data rates than have previously been available.
FIG. 1 shows a table describing a number of wireless communications bands in the wireless spectrum. One or more of the wireless communications bands may be used, for example, in a CDMA, GSM, LTE, or LTE-advanced equipped mobile device. The first column indicates the operating band number for each one of the operating bands. The second and third columns indicate the uplink and downlink frequency bands for each one of the operating bands, respectively. Finally, the fourth column indicates the duplex mode for each one of the operating bands. In non-carrier aggregation configurations, a mobile device will generally communicate using a single portion of the uplink or downlink frequency bands within a single operating band. In carrier aggregation applications, however, a mobile device may aggregate bandwidth across a single operating band or multiple operating bands in order to increase the data rate of the device.
FIG. 2A shows a diagram representing a conventional, non-carrier aggregation configuration for a mobile device. In the conventional configuration, a mobile device communicates using a single portion of the wireless spectrum 10 within a single operating band 12. Under the conventional approach, the data rate of the mobile device is constrained by the limited available bandwidth.
FIGS. 2B-2E show diagrams representing a variety of carrier aggregation configurations for a mobile device. FIG. 2B shows an example of contiguous, intra-band carrier aggregation, in which the aggregated portions of the wireless spectrum 14A and 14B are located directly adjacent to one another and are in the same operating band 16. FIG. 2C shows an example of non-contiguous intra-band carrier aggregation, in which the aggregated portions of the wireless spectrum 18A and 18B are located within the same operating band 20, but are not directly adjacent to one another. FIG. 2D shows an example of inter-band carrier aggregation, in which the aggregated portions of the wireless spectrum 22A and 22B are located in different operating bands 24, 26. A modern mobile device should be capable of supporting each one of the previously described carrier aggregation configurations. Finally, FIG. 2E shows an example of inter-band carrier aggregation across three operating bands, in which the aggregated portions of the wireless spectrum 21A, 21B, and 21C are located in different operating bands 23, 25, and 27. Additional carrier aggregation configurations may aggregate bandwidth across four or more operating bands.
The use of carrier aggregation may pose unique problems for the front end circuitry in a mobile device. For instance, a mobile device using carrier aggregation may require two or more antennas. The use of more than one antenna may complicate the design of the front-end switching circuitry within the mobile device. Additionally, the use of carrier aggregation across certain operating bands may cause undesirable interference between transmit and receive circuitry in a mobile device front end that renders the mobile device unusable in these operating bands.
FIG. 3 shows conventional front end circuitry 28 for use in a mobile terminal. The front end circuitry 28 includes antenna switching circuitry 30, a diplexer 32, and an antenna 34. The antenna switching circuitry 30 includes low band switching circuitry 36 and high band switching circuitry 38. The low band switching circuitry 36 is adapted to couple one of a first plurality of RF front end ports 40 to the antenna 34 through the diplexer 32. The high band switching circuitry 38 is adapted to couple one of a second plurality of RF front end ports 42 to the antenna 34 through the diplexer 32. The diplexer 32 includes a low band port 44 coupled to the low band switching circuitry 36, a high band port 46 coupled to the high band switching circuitry 38, and an antenna port 48 coupled to the antenna 34. The diplexer 32 is adapted to pass high band signals falling within a high pass band between the high band port 46 and the antenna port 48, pass low band signals falling within a low pass band between the low band port 44 and the antenna port 48, and attenuate signals outside of the high and low pass bands. Although effective at selectively placing the antenna 34 in communication with the appropriate RF front end port, the conventional front end circuitry 28 shown in FIG. 3 is not suitable for carrier aggregation applications that require multiple antennas.
FIG. 4 shows conventional front end circuitry 50 for use in a mobile terminal with two antennas. The front end circuitry 50 includes antenna switching circuitry 52, a first diplexer 54A, a second diplexer 54B, a first antenna 56A, and a second antenna 56B. The antenna switching circuitry 52 includes first antenna switching circuitry 52A and second antenna switching circuitry 52B. The first antenna switching circuitry 52A includes first low band switching circuitry 58, first high band switching circuitry 60, second low band switching circuitry 62, and second high band switching circuitry 64. The first low band switching circuitry 58 and the first high band switching circuitry 60 are adapted to selectively couple one of a first plurality of RF front end ports 66 to the second antenna switching circuitry 52B through the first diplexer 54A. The second low band switching circuitry 62 and the second high band switching circuitry 64 are adapted to selectively couple one of a second plurality of RF front end ports 68 to the second antenna switching circuitry 52B through the second diplexer 54B. The second antenna switching circuitry 52B includes antenna selection circuitry 70, which is adapted to selectively place the first antenna 56A and the second antenna 56B in communication with either the first diplexer 54A or the second diplexer 54B.
The antenna switching circuitry 52 may comprise a plurality of transistors and other assorted passive components. As is well known in the art, non-linearity of the transistors and other passive components within the antenna switching circuitry 52 may generate harmonic distortion about a passing signal. In certain carrier aggregation configurations, the generated harmonic distortion can cause desensitization of receive circuitry in the conventional front end circuitry 50 illustrated in FIG. 4. For example, the conventional front end circuitry 50 may experience problems in a carrier aggregation configuration using bands 3 and 8 (CA 3-8). In a CA 3-8 configuration, the conventional front end circuitry 50 will couple one of the second plurality of RF front end ports 68 corresponding with the band 8 transmit port to the antenna selection circuitry 70 in order to transmit a carrier signal between 880-915 MHz. As the carrier signal passes through the first low band switching circuitry 58, harmonic distortion is generated. The carrier signal and harmonic distortion travel through the first diplexer 54A, where the harmonic distortion is effectively filtered. However, as the carrier signal travels through the antenna selection circuitry 70, additional harmonic distortion is generated.
Because at least a portion of the second harmonic of the band 8 uplink band (1760-1830 MHz) falls within the band 3 downlink band (1805-1880 MHz), components of the harmonic distortion about the second harmonic are within the high pass band of the first diplexer 54A, and a portion of the harmonic distortion will be delivered to the first high band switching circuitry 60. Further, because the front end circuitry 50 is configured to simultaneously transmit on band 8 and receive on band 3, one of the first plurality of RF front end ports 66 corresponding with the band 3 receive port will be coupled to the first diplexer 54A through the first high band switching circuitry 60. Accordingly, a portion of the distorted band 8 transmit signal about the second harmonic will be delivered to the band 3 receive circuitry, where it will cause desensitization. Additionally, the harmonic distortion in the carrier signal will be presented to the antennas 56A and 56B, thereby degrading the quality of the wireless signal. As a result of the desensitization of the receiver circuitry, the performance of the front end circuitry 50 illustrated in FIG. 4 may suffer in a CA 3-8 configuration.
As an additional example, the conventional front end circuitry 50 will also experience problems in carrier-aggregation applications using bands 4 and 17 (CA 4-17), because the third harmonic of a band 17 transmit signal (2112-2148 MHz) falls within a band 4 receive signal (2110-2155 MHz). The problem with the conventional front end circuitry 50 may occur in any carrier aggregation configuration using operating bands in which the harmonic components of the carrier signal fall within the frequency band of the receive signal. The limited combination of operating bands usable in a carrier aggregation configuration by the conventional front end circuitry 50 illustrated in FIG. 4 may impede the performance and versatility of a mobile device.
In addition to the problems encountered by the conventional front end circuitry 50 when one or more harmonics of a transmit signal fall within a receive operating band, the conventional front end circuitry 50 is also limited to inter-band carrier aggregation applications, in which the transmit signal and the receive signal are located in different operating bands that are separated by a certain frequency delta. Because the conventional front end circuitry 50 includes only two antennas, each one of the antennas 56 must be used to simultaneously receive signals within a first carrier aggregation operating band and a second carrier aggregation operating band. Accordingly, the diplexers 54 must separate each incoming RF signal so that they may be routed to the correct receiving circuitry in the conventional front end circuitry 50. In order for the diplexers 54 to properly separate incoming RF signals, the operating bands of the received RF signals must be separated by a certain frequency delta, as determined by the filter response of the diplexers 54. Generally, one of the received RF signals must be a high band signal, while the other received RF signal must be a low band signal. If the signals are not separated by an appropriate frequency delta, the received signals will not be separated by the diplexers 54, and both signals will be passed to the same receive circuitry in the conventional front end circuitry 50. Accordingly, the conventional front end circuitry 50 cannot operate in either contiguous or non-contiguous intra-band carrier aggregation applications.
A further challenge presented by the conventional front end circuitry 50 is the wide band antennas 56 required for proper operation of the circuitry. Due to the fact that the conventional front end circuitry 50 uses a single antenna to simultaneously receive both low band and high band signals, the antennas 56 must be operable over a wide bandwidth. Creating such wide bandwidth antennas generally requires tunable components and high order filters, which generally add to the complexity and cost of a mobile terminal, and may introduce additional insertion loss into the RF signal path.
FIG. 5 shows an exemplary configuration of a mobile device 72 including four antennas 74. For context, a battery 76, a speaker 78, and a charging port 80 are also shown. As shown in FIG. 5, each antenna 74 in the mobile device 72 is placed in a corner of the device. Accordingly, each one of the antennas 74 is separated from the others by some physical distance. Due to the orientation of the mobile device 72, for example, in a user's hand, one of the antennas 74 may experience a higher transmit efficiency and/or higher receive sensitivity than the others. As the orientation of the mobile device 72 changes, the most efficient or sensitive antenna may also change. In order to optimize the performance of the mobile device 72, front end circuitry within the mobile device 72 should be capable of dynamically selecting the most efficient antenna for transmission and reception of wireless signals.
Accordingly, there is a need for front end circuitry that is capable of operating in all carrier aggregation configurations while reducing cross-distortion between signals, and is further capable of antenna swapping to optimize the performance of a mobile device.